Magneto generator



March 5, 1940. A. E. WOODRUFF MAGNETO GENERATOR Filed April 16. 1937 2 Sheets-Sheet 1 FIG. i

FIG. 4

J 44 J a m w 0% \MO 1 A m M W w FIG'. 3

FIG. 2

INVENTOR. ALBERT E, WOVODRUFF ATTORNEY;

March 5, 1940. A. E. WOODRUFF 2,192,215

MAGNE'IYO GENERATOR Filed April 16, 1937 2 Sheets-Sheet 2 STATION A STATION 8 FIG. 7 Z

I l l 1o so so so MILL r- SECONDS INVENT OR. ALBERT E. WOODRUFF ATTORNEY.

Patented Mar. 5, 1940 UNITED STATES HAGNETO GENERATOR Albert E. Woodrufl', Oak Park, lll., assignor to Associated Electric laboratories, Inc., Chicago, 111., a corporation of llelawarc Application April 16, 1931, Serial No. 137,274

12 Claims.

This invention relates in general to magneto generators or transmitters but more particularly to generators arranged to be used for signalling purposes in communication systems.

6 It is an object of the invention to provide a magneto generator capable of transmitting an output frequency of signalling current over a line to a telephone receiver so as to actuate the same in a distinct and audible manner whereby 10 the receiver serves as acall signal.

A further object is to devise a signalling generator adapted for manual operation in which a relatively constant high frequency voltage is produced which is independent of the manual oper- 15 ating speed of the generators.

A further object is to arrange a magneto generator in which the output frequency may be easily varied by a' simple adiustment of the device.

Further objects attained by the device are com- 20 pactness and simplification of the various parts tending to reduce the number of moving elements, and also theease of adjustment and assembly.

In the contemplated or preferred form of the 25 invention a permanent magnet is provided between the poles of which a coil winding and spaced pole shoes are arranged. A relatively stifi reed is secured and adjustably anchored at one end and extends through the coilbetween-the 30 pole shoes. Opposite the free end of the reed a cam wheel havinga plurality of teeth thereon is arranged on the shaft with a handle so the cam wheel can be manually rotated. Upon rotation of the cam wheel the teeth are caused to r 35 pluck the end of the reed in rapid succession resulting in vibration of the reed each time with diminishing amplitude until the next cam tooth plucks the reed. The vibration of the reed varies the magnetic flux flowing between the pole shoes 40 thereby generating a corresponding flow of currentthrough the surrounding coil winding, the ends of which may be connected to a suitable line circuit and signal whereby the current may be used to actuate the signal with recurring fre- 45 quency. In the preferred form the signal may be the unit employed in a magnetic type of telephone.

The preferred embodimentof the invention is illustrated in the accompanying sheets of draw- 50 ings in which:

Fig. 1 shows a top view of the magnet generator;

Fig. 2 is a side elevation of the same; Fig. 3 is an end view along the section line 56 8-3 of F18. 2;

Fig. 4 is a cross-sectional top view of a portion of the apparatus taken along the line H of Fig. 2;

Fig. 5 is a diagrammatic showing of the magnetic circuit paths through the device; 5 Fig. 6 is a graph showing the frequency wave form of the generator output; and

Fig. 'l is a schematic circuit arrangement of a telephone and signalling system including the magneto .transmitter of .the invention. 10

Referring now more particularly to Figs. 1 to 4, the detailed mechanical construction of a preferred form of magneto transmitter embodying the invention will be described. A suitable mounting plate I is provided for the device having mounting holes therein for fastening the unit in any desired position or location. A pair of bearing posts 2 and I for journalling the rotatable shaft 4 at their upper ends are secured at their lower ends to mounting pate l by the countersunk screws such as l. A collar 5 on shaft 4 adjacent post 2 retains the shaft in its set position while a manually operable handle 6 attached to the end of the shaft provides means for rotatably actuating the shaft. In a contemplated arrangement any other suitable driving means .such as a motor may be attached to the shaft 4 to rotate it. A cam wheel 8 having a series of teeth 9 around its periphery is securely fastened to the shaft I by a set screw so that it is rotatable with the shaft when the handle 8 is turned.

A horseshoe type permanent magnet I I ,is secured to the mounting plate I by screws 26 and 21 in such a position that the legs of the magnet extend toward the shaft 4. Centrally located and between the legs of the magnet is a relatively stiff and heavy vibratable steel reed ii the free end of which is positioned directly under the shaft 4 in the path of movement. of the cam teeth 9 as seen in Fig. 2. The other end of the 40 reed I l is rigidly clamped between the non-magnetic clamping blocks l2 and 13 by a pair of screw-bolts I4 and i5, extending through holes in the clamping blocks and threaded into the mounting plate I. One leg of the magnet II is positioned under the clamping block I! and is thereby clamped to the mounting plate i by the screws II and I5. Each of the, clamping blocks l2 and II has a pair of. narrow edges ii along adjacent sides in contact with the reed ii so that a flat, smooth and relatively narrow edge engages the reed, ensuring accurate, rigid clamping of the reed. The reed is free to vibrate at its front end while the opposite end is rigidly anchored to the base as described.

An electromagnetic coil winding 20 is arranged between the legs of the permanent magnet in front of the clamping blocks l2 and I3. The winding is placed on an insulated spool 2| having an opening therein through which the reed ll extends. A non-magnetic sleeve 22 lines the opening through which the reed extends in order to protect the coil spool and accurately define the K opening. The opening is of suflicient size so 10 that the reed in its vibrations will never come into contact with or strike against the sleeve 22.

A pair of oppositely disposed pole shoes 24 and 25 are arranged on either side of the coil 20 with their fiat surfaces engaging the magnet legs.

Pole shoe 24 is secured to one leg by the screw 26 while the pole shoe 25 is held to the other magnet leg by screw 21 which 'screw also extends through the mounting plate I and the magnet leg to assist in securing the magnet and other 20 parts to the mounting base I. The open ends of the pole shoes are arranged on opposite sides and spaced from the reed ll only a suflicient distance so that the reed will not strike against the 25 pole shoe edges when it is actuated. The ends of the pole shoes present opposite polarities of the permanent magnet to the opposite surfaces of the reed.

By arranging the pole shoes, coil winding, and reed anchoring means inside and. between the ends of the permanent magnet a very compact unit is provided which occupies a small mounting space and which is easily assembled. The clamping blocks l2 and 13 in addition to anchoring the reed hold the permanent magnet securely to the base plate I through the medium of screws l4 and I5.

The operation of the magneto transmitter will now be pointed out, having in mind the struco tural details of the unit just described. Rotation of the handle either manually or otherwise in a clock-wise direction turns the shaft 4 and with it the cam wheel 8. The teeth of the cam wheel thereby successively engage the free end of the stifi reed II and as each tooth engages the reed it presses it downward a distance according to the length of the tooth and slides along a portion of the reed until it snaps off the end. The limit of the downward movement of the reed by the' tooth is such that the reed does not touch the sides of the opening surrounding it or the pole shoes. After the tooth snaps of! the end of the -reed which now has considerable tension stored in it, the reed, due to its resiliency, vibrates for u a time interval with diminishing amplitude. The initial vibrations are of such an amplitude that the reed will not touch either the portion of the cam wheel between the teeth 9 or the pole shoe ends. As shown, the reed II is constructed of go somewhat heavy material and therefore is relatively stiff so that it requires a fairly large amount of energy to operate or pluck it, enabling it to vibrate for a certain interval of time. The teeth 9 are spaced apart on the cam wheel a suflicient 66 distance so that the reed is nearly restored to its stationary normal state after having been vibrated and before a succeeding tooth plucks it again. A small portion of the diminishing yibrations, however, are damped due to the next tooth 70 engaging the reed and pressing it downward preceding the interval that it snaps off the end of the reed. The graph, Fig. 6, shows the general wave form of the output of the generator when operated at normal speed. A representative out- !6 put suitable for signalling use is one comprising than between the poleshoes closest in proximity a value of 10 miliwatts with a frequency of 1100 cycles at 25 volts.

In order that the amplitude and vibration of the reed may be accurately controlled the device contemplates a simple adjustment feature. 5 Where it is desired to regulate the output frequency of the generator so that the signal to be actuated thereby is responsive with a diflerent degree of audibility, or where a change in the responsive tone of the unit is required, the screws 10 I4 and I5 are loosened so that the clamping areas l5 are disengaged from anchorage of the end, of the reed II and the reed is moved the desired amount, either to the left (Fig. 2) or to the right, after which the screws are again tightened. This 15 results in the reed being rendered more still. or flexible and thereby its output frequency is varied when plucked. The extent to which the reed end is moved must be such, however, that it is not placed out of range of the teeth 9 of the cam wheel 8. Only a slight movement is needed to effect a change and the frequency generated by the reed when once set is independent of the rate of speed at which it is plucked.

Fig. 5 shows schematically the magnetic flux paths extending through the generator whereby the displacement of the reed varies the direction of the flux through the reed, thereby generating a current flow in the coil winding first in one direction and then in the reverse direction. It

will be noted that the extent of vibration of the reed is somewhat less between the pole shoes adjacent to the point where the reed is anchored to the free end of the reed. A relatively large change is produced in the reluctance of the magnetic circuit path and therefore a current of relatively large magnitude is induced in the coil winding.

A practical utility for the device according to a the invention will now be pointed out by referring to the circuit arrangement in Fig. 7, wherein no current supply source is required for either talking or signalling. A magnetic type of telephone apparatus diagrammatically shown at station A a with the reference TA is normally connected to the line conductors L through closed contacts of the manually operable key KA. Sstation B having the unit TB is similarly connected to the line through key KB. A magneto generator or signailing device SA constructed according to the invention and shown diagrammatically, is connected to the line L through the operation of key KA for the purpose of signalling the station B. The signalling device SB at station B is also connected to the line to signal station A upon operation of the associated key KB.

The telephonic apparatus TA and TB is of the magnetic type which is well known in the art and comprises essentially a cone-shaped diaphragm 42 mechanically connected to a pivoted armature 4| positioned between the pole pieces of the permanent magnet 43 and surrounded by coil winding 40. The units TA and TB, for example, are arranged so that they may be used as combination .5 transmitters and receivers. Speech waves impinging upon the diaphragm 42 of device TB actuates armature 4| between the pole pieces of magnet 43 thereby varying the magnetic flux and inducing a corresponding current flow in the coil winding 40 which traverses the line conductors L and inversely actuates the magnetic telephone unit TA at the station A as a receiver. In order to signal the station B the magneto generator SA at station A is operated to generate a series of relatively high frequency impulses of gradually diminishing amplitude which are transmitted over the line L through the operated contacts of actuated key KA, and operate the diaphragm 42 of the unit TB at station B to produce a loud audible signal so as to attract the attention of the person at station B to the call. By providing the locking type keys KA and KB the signalling generators SA and RB are connected to theline L only when signalling is to take place.

, Restoration of the key connects the telephone units to the line and conversation over them may take place.

It will therefore be seen that I have provided a very simple and yet highly eflicient type of generator for generating a tone signal and one which is especially useful in a system employing magnetic telephones for speech.

Having described the various features of my improved device, what I consider to be novel will be pointed out in the appended claims.

What is claimed is:

1. In a magneto generator, a permanent magnet having a pair of pole shoes thereon, a coil windthe other end extends between said pole shoes sitioned between said pole shoes, means for rigidly supporting one end of said armature between the legs of said permanent magnet, the other end of said armature projecting through said coil winding and being free to vibrate between the pole shoes on each side thereof, means for actuating the free end of said armature to vibrate the same, and means for recurrently actuating said armature at its predetermined frequency.

3. In a magneto generator, a permanent magnet having a pair of pole shoes secured opposite each other to the ends of the magnet, an armature positioned between the ends of said pole shoes, means for rigidly clamping one end. of said armature at one side of said pole shoes, a coil winding between said pole shoes having an opening therein through which said armature extends,

said armature having a predetermined vibratory frequency of operation, means for actuating the free end of said armature at the end opposite that at which it is rigidly supported, said armature-actuating means comprising a cam wheel having projections thereon for recurrently actuating said armature, and means for operating said "cam wheel.

4. In a magneto generator as claimed in the preceding claim, the provision. of means for ad- J'ustably varying the frequency of said vibratory armature-by variably arranging the armature supporting means.

5. In a magneto generator, a permanent magnet having a pair of pole shoes secured to the ends of the magnet and opposite each other, a vibratory armature extending between the poles of said pole shoes, a coil winding surrounding said armature between said pole shoes, means for clamping said armature at one of its ends and said permanent magnet to said supporting plate, a coil winding surrounding said armature, and means for successively actuating the free end of said armature to vibrate it between the poles of said pole shoes and thereby induce a current flow in said coil winding.

'1. In a magneto generator, a permanent magnet having opposite spaced pole shoes attached thereto, a vibratory armature positioned between the ends of said pole shoes, means for rigidly clamping one end of said armature, said armature having a frequency rate of operation which is predetermined, means for recurrently actuating the free end of said armature to vibrate the same between the said pole shoes at a frequency, the rate of frequency of said armature being independent of the recurring actuation of its free end.

8. In a magneto generator as claimed in the preceding claim in which the frequency of vibration of the armature produces a current flow in said coil winding which corresponds in frequency to that of the vibration of the armature and the recurrency of operation of the free end of the same.

9. In a magneto generator having a permanent magnet and pole shoes attached thereto, a vibratory reed armature positioned between said pole shoes, clamping means for rigidly supporting one end of said armature, said clamping means comprising clamping blocks having two parallel flat surfaces engaging opposite sides of said armature for clamping the armature at two separate points, a coil winding surrounding said armature, means for recurrently actuating the free ,end of said armature to cause it to vibrate between said pole shoes, said armature vibrating with a diminishing amplitude each time after being actuated, and a common mounting plate for said armature actuating means, said clamping means, and said permanent magnet.

10. In a magneto generator, a permanent magnet of the horseshoe type, U-shaped pole shoes attached to each of the legs of said magnet, the

legs or said pole shoes projecting toward each other between the ends of said magnet, an armature extending between the free end of said U-shaped pole shoes, clamping means arranged opposite one of the legs of said pole shoes and between the legs of said permanent magnet for rigidly supporting one end of said armature, a.- cam wheel having a series of teeth around its periphery, means for rotating said cam wheel, means for supporting said cam wheel and actuating means opposite the free end of said armature in position for vibrating the same recurrently, said cam wheel and operating means being positioned opposite the ends of the legs of said permanent magnet, and a common mounting plate for supporting said apparatus.

11. In a magneto generator having pole shoes and an armature, means for rigidly clamping one end of said armature in pofltion between the magnetpoleshoeaacoilwindingsurrounding" said armature, a cam wheel having successive for inducing a current flow in the coil winding teeth around its periphery positioned opposite the surrounding the same. free end of said armature, means for actuating 12. In a magneto enera r 88 claimed in said cam wheel to successively engage the teeth claim 1, in which the means for. anchoring one 5 with the armature to periodically vibrate the end of said armature may be readily adjustable 6 same, said armature-having a vibratory frequency for altering the vibrating length of the armature of a particular value, the amplitude of which (11- and thus the frequency of the induced current minishes each time after the armature is actuin said windings. 1 ated by the cam wheel teeth, and means respon- 10 sive to the frequency vibration of said armature ALBERT E. WOODRUFF. l0 

